The 1, 4-benzodiazepines (BZD's) such as flunitrazepam (FNZM), flurazepam and diazepam are minor tranquilizers, anticonvulsants, and skeletal muscle relaxants which probably act by enhancing inhibitory neuronal activity in the central nervous system. We have shown that the chemosensitivity of embryonic chick-spinal cord (SC) neurons in dissociated cell culture to g-aminobutyric acid (GABA) is enhanced by treatment with BZD's as expected from work in the intact CNS. The binding affinities of radio-labelled BZD's was determined in membrance homogenates of 20-day embryonic chick brain (EBM) and spinal cord (ESM) are about three orders of imagnitude greater than expected on the basis of in vivo studies and 35-fold greater than predicted from potentiation of GABA chemosensitivity in SC cultures. The differences between the experimental conditions used in binding assays and electrophysiology will be investigated. A SC culture membrane binding system will be established in which combined biochemical and electrophysiological experiments will be carried out. We have found high and low affinity binding of BZD's to 7-day EBM and ESM, in which the high affinity site is similar to that observed in 20-day EBM and ESM. The high affinity site is selectively and irreversibly inactivated by photoaffinity labeling with FNZM. The relationship between BZD binding and enhancement of GABA chemosensitivity will be investigated on intact SC neuronal cell cultures. We wish to determine whether high affinity receptor binding of BZD results in enhanced GABA action. In the long-term, the distribution, turnover and possible regulation of BZD receptors during development shall be investigated.